[Navigation Experiment] Add WKBasedNavigationManagerImpl.

ios/web/navigation/navigation_manager_delegate.h

Index: ios/web/navigation/navigation_manager_delegate.h
diff --git a/ios/web/navigation/navigation_manager_delegate.h b/ios/web/navigation/navigation_manager_delegate.h
index 90c7675c057dbe66f4fb3fee2fe05244a4faba5d..d5f91f62768b73cddd53b81eeaa4e6a1d7865c53 100644
--- a/ios/web/navigation/navigation_manager_delegate.h
+++ b/ios/web/navigation/navigation_manager_delegate.h
@@ -5,7 +5,9 @@
 #ifndef IOS_WEB_NAVIGATION_NAVIGATION_MANAGER_DELEGATE_H_
 #define IOS_WEB_NAVIGATION_NAVIGATION_MANAGER_DELEGATE_H_
 
+#import <WebKit/WebKit.h>
 #include <stddef.h>
+#include <memory>
 
 #import "ios/web/public/navigation_manager.h"
 
@@ -13,6 +15,7 @@ namespace web {
 
 struct LoadCommittedDetails;
 class WebState;
+class WebViewNavigationProxy;
 
 // Delegate for NavigationManager to hand off parts of the navigation flow.
 class NavigationManagerDelegate {
@@ -42,6 +45,9 @@ class NavigationManagerDelegate {
 
   // Returns the WebState associated with this delegate.
   virtual WebState* GetWebState() = 0;
+
+  // Returns the main WKWebView used to display web content.
+  virtual WebViewNavigationProxy* GetWebViewNavigationProxy() const = 0;

[Eugene But (OOO till 7-30), 2017/06/27 22:02:00]

Would it make sense to have
WKBasedNavigationManagerImpl::SetWebViewNavigationProxy instead? We probably not
going to use NavigationManagerDelegate inside WKBasedNavigationManagerImpl
anyway, so at some point the delegate may be removed. 

[danyao, 2017/06/28 22:11:04]

I prefer this over SetWebViewNavigationProxy for a couple of reasons:
1) We still need NavigationManagerDelegate inside the new navigation manager for
notifying observers.
2) CRWWebController might not always have the same WKWebView object. The getter
provides a convenient place to update the point before giving the proxy to
WKBasedNavigationManagerImpl.

[Eugene But (OOO till 7-30), 2017/06/29 01:48:18]

It's just somewhat strange that delegate has Get<Something> method (I know it
already has GetWebState, but that's existing code). Not a big deal though.

If we going to keep the delegate, then maybe we should move all methods from
WebViewNavigationProxy to NavigationManagerDelegate? I'm fine with the code as
it is because it is temporary anyway.

 };
 
 }  // namespace web